In radiotelephone systems, subscribers transmit at multiple power levels to maintain communication to a base-station as the subscriber moves throughout a particular coverage area. The use of multiple power levels is necessary because, as a subscriber moves away from the base-station it is communicating with, its effective received signal strength as measured by the base-station decreases. When the received signal strength falls below a particular threshold, the quality of communication may begin to degrade. To avoid the degradation, the base-station will instruct the subscriber to transmit at the next highest power level. This effectively increases the received signal strength of the subscriber transmission as measured by the base-station, thus avoiding the signal quality degradation.
As reuse patterns become closer and closer together, a restriction on the power level that the subscriber transmits is required. This is typically accomplished by setting a parameter that defines the maximum power level (MAXPL) the subscriber can transmit while it is being serviced by the current source base-station in a given sector/cell. The parameter is typically determined at the cell site planning stages and is typically set so that the maximum allowable power level that the subscriber is able to transmit at is below the available power level of the subscriber. This is done so that the subscriber causes the least amount of interference to neighboring coverage areas during its transmission.
A problem arises however, when a subscriber goes into a somewhat concealed infrastructure, a parking garage or a building for example. Since the power level is restricted to the MAXPL level, the probability of the subscriber being able to communicate to the source base-station decreases. In addition, the MAXPL algorithm used at the source base-station limits the power level all the time, instead of only when the mobile is out of the coverage area of the serving cell. This problem, initially implemented to decrease interference between neighboring coverage areas, has lead to an increased number of dropped calls.
Thus, a need exists for a radiotelephone system which allows the subscriber to transmit above the MAXPL limit when the subscriber is in the best sector/cell while still limiting the amount of interference caused by the subscriber during typical radiotelephone operation.